From 10 to 20% of acquired aplastic anemia survivors will develop a clonal disease within the decade following their diagnosis as will up to 40% of children and young adults with the inherited bone marrow failure syndrome Fanconi anemia. Recent work from the laboratories of the applicants and from other centers leads to the conclusion that clonal evolution in aplastic states arises in the context of ongoing stem cell damage through a process of clonal selection and adaptation. In the past year the two applicants have each independently developed a unique murine model of clonal evolution in Fanconi anemia. The applicants propose herein to use these models to identify the earliest molecular events involved in clonal evolution of FA stem cells. These models provided material for genome wide expression analyses which, when combined with our recently completed studies on the human bone marrow transcriptome, have not only confirmed the adaptive nature of clonal selection in this disease but have yielded common candidate genes, the potential of one of which (HoxA9) to facilitate clonal selection of adapted cells has been established in preliminary studies. A second family of genes has potential to explain the molecular underpinnings of the random aneuploidy that is characteristic of MDS in FA. Collectively, our goals are to identify genetic and epigenetic causes of clonal evolution in vitro and in vivo. We anticipate that by doing so, we can use the knowledge to develop strategies for prevention of clonal evolution in patients at high risk. We will use murine and human FA cells that have not undergone clonal evolution (FAAPL) and FA cells that have clonally evolved (FACL). PUBLIC HEALTH RELEVANCE: This application seeks to identify molecular mechanisms that underlie the development of myeloid malignancies and aplastic anemia. Information learned from this application may provide insights into the treatment of myelodys plasia and acute myelogenous leukemia. These are hematopoietic malignances that are important in adults and particularly the elderly as well as in children with a genetic disorder called Fanconi Anemia.